Marsh rice rat: Wikis


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Marsh rice rat
Fossil range: Rancholabrean (300,000 years before present) – present
A rat, grayish above and pale below, seen from above and from the front, among reed and leaf litter.
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Genus: Oryzomys
Species: O. palustris
Binomial name
Oryzomys palustris
(Harlan, 1837)[2]
Map of the eastern United States and nearby areas. The marsh rice rat occurs along the coast from southern Texas to New Jersey and inland to Missouri. Oryzomys couesi occurs in southernmost Texas and nearby Mexico.
Distribution of the marsh rice rat (blue) in the eastern United States. A small part of the distribution of Oryzomys couesi is also shown (red).
  • Mus palustris Harlan, 1837[2]
  • Arvicola oryzivora Bachman, 1854[3]
  • Oryzomys palustris: Baird, 1857[4]
  • Oryzomys palustris natator Chapman, 1893[5]
  • Oryzomys palustris texensis J.A. Allen, 1894[6]
  • Oryzomys palustris coloratus Bangs, 1898[7]
  • Oryzomys natator floridanus Merriam, 1901[8]
  • Oryzomys fossilis Hibbard, 1955[9]
  • Oryzomys palustris planirostris Hamilton, 1955[10]
  • Oryzomys palustris sanibeli Hamilton, 1955[11]
  • ?Oryzomys argentatus Spitzer and Lazell, 1978[12]

The marsh rice rat (Oryzomys palustris) is a North American rodent in the genus Oryzomys of family Cricetidae.

It is found only in the southern and eastern United States, ranging from New Jersey to Texas. The population in the Florida Keys is sometimes regarded as a separate species, Oryzomys argentatus. Its natural habitats are subtropical or tropical swamps, subtropical or tropical seasonally wet or flooded lowland grassland, swamps, and saline marshes.[1]



The marsh rice rat is classified as one of eight species in the genus Oryzomys, which is distributed from the eastern United States (marsh rice rat) into northwestern South America (O. gorgasi).[14] Oryzomys previously included many other species, which were progressively removed in various studies culminating in contributions by Marcelo Weksler and coworkers in 2006 that removed more than forty species from the genus.[15] All are classified in the tribe Oryzomyini ("rice rats"), a diverse assemblage of American rodents of over a hundred species,[16] and on higher taxonomic levels in the subfamily Sigmodontinae of family Cricetidae, along with hundreds of other species of mainly small rodents.[17]


Early history

The marsh rice rat was discovered in 1816 in South Carolina by John Bachman.[18] Bachman intended to describe the species as Arvicola oryzivora, but sent a specimen to Richard Harlan and Charles Pickering at the Academy of Natural Sciences in Philadelphia to confirm its identity.[19] Another specimen, from New Jersey, was found in the Academy's collection, and Harlan took it upon himself, against Pickering's wishes, to describe the new species as Mus palustris, proclaiming it one of the few true rats of the United States.[20] In 1854, in The quadrupeds of North America, Bachman redescribed it as Arvicola oryzivora, considering it more closely related to the voles then placed in the genus Arvicola, and also recorded it from Georgia and Florida.[19] Three years later, Spencer Fullerton Baird argued that the referral of the species to Arvicola was erroneous and introduced a new generic name for the marsh rice rat, Oryzomys, which was then recognized either as a full genus or as a subgenus of the now-defunct genus Hesperomys.[21] Since the 1890s, Oryzomys has been recognized as a distinct genus, with the marsh rice rat (Oryzomys palustris) as its type species.[22]

Species boundaries and subspecies

In the 1890s, several subspecies of the marsh rice rat were described from the United States: natator from Florida in 1893,[5] texensis from Texas in 1894,[6] and coloratus from elsewhere in Florida in 1898.[7] Clinton Hart Merriam recognized the former two as separate species in 1901 and described a subspecies of natator, floridanus.[23] In his 1918 revision of North American Oryzomys, E.A. Goldman again recognized all these as a single species, Oryzomys palustris, with four subspecies, which he said formed a "closely intergrading series".[24] He synonymized floridanus under coloratus.[25] Two additional subspecies were described by W.J. Hamilton in 1955 from Florida islands: planirostris from Pine Island[10] and sanibeli from Sanibel Island.[11] Also in 1955, C.W. Hibbard described a new species of Oryzomys, O. fossilis, from Pleistocene deposits in Kansas, on the basis of small differences in characters of the tooth with living marsh rice rats,[9] but this species, later also found in Texas, has since been demoted to a subspecies, because fossilis does not differ more from living marsh rice rats than the latter differ from each other.[26]

Merriam and Goldman had recognized that a number of Central American species, including Oryzomys couesi and numerous forms with more limited distributions, are related to the marsh rice rat.[27] O. couesi ranges north to southernmost Texas, where its distribution meets that of the marsh rice rat. In 1960, E.R. Hall argued that specimens from the contact zone were intermediate between the local forms of O. couesi and the marsh rice rat, and accordingly included the former in the marsh rice rat.[28] While reporting on the ecology of Texan O. couesi in 1979, Benson and Gehlbach noted that populations of O. couesi and the marsh rice rat there were in fact distinct, with the latter being smaller and less brownish in color; their karyotypes were also distinct.[29] Since then, the two have generally been retained as distinct species, as supported by further research; a 1994 study even found the two to occur at some of the same places (in sympatry) in southern Texas and nearby Tamaulipas, Mexico.[30]

In 1973, rice rats were discovered at Cudjoe Key in the Florida Keys, and in 1978 Spitzer and Lazell described the population as a new species, Oryzomys argentatus.[12] The status of this form—either a distinct species[31] or not even subspecifically distinct from O. palustris natator[32]—has remained controversial since; the 2005 third edition of Mammal Species of the World does not recognize O. argentatus as a separate species, but acknowledges a need for further research.[33] There is also disagreement on the number of subspecies: a 1989 morphometrical study could distinguish only two—natator from much of Florida (including coloratus, planirostris, sanibeli, and floridanus, as well as argentatus) and palustris from the rest of the range (including texensis), while others have retained more of the described subspecies.[34]

Common names

Many common names have been proposed for the marsh rice rat. Early describers used "Rice Meadow-Mouse"[3] and "Rice-field Mouse".[35] Goldman used different common names for each of the subspecies he recognized: "Swamp Rice Rat" for O. p. palustris,[24] "Central Florida Rice Rat" for O. p. natator,[36] "Everglades Rice Rat" for O. p. coloratus,[25] and "Texas Rice Rat" for O. p. texensis.[37] Other more recently used common names include "marsh oryzomys"[38] and "swamp rice rat".[39]


The marsh rice rat is a medium-sized rodent that looks much like the common black and brown rats.[40] The upperparts are generally gray to grayish brown, with the head a bit lighter, and the underparts are off-white, as are the feet. The tail is dark brown above and may be paler below.[41]

There is some geographic variation in fur color: western populations (texensis) are lighter than those from the east (nominate palustris), and Florida populations are generally more tawny or reddish than either, with those from southern Florida (coloratus) brighter than those from the center of the state (natator).[42] The Florida Keys form (argentatus) is silvery,[43] and the two other Florida island forms—planirostris and sanibeli—lack the reddish tones of mainland Florida populations and are instead grayish, resembling nominate palustris (planirostris), or brownish (sanibeli).[44] In 1989, Humphrey and Setzer reviewed variation in color among Florida populations. They found argentatus to be substantially lighter and planirostris and sanibeli to be somewhat darker than mainland populations, and argentatus to have a less yellow fur, but found no significant differences in redness. There was also significant variation within populations.[45]

Distribution and habitat

The marsh rice rat currently occurs in much of the eastern and southern United States, northeast to southern New Jersey and southeastern Pennsylvania, and south to southeastern Texas and far northeastern Tamaulipas, Mexico.[46] The northernmost records in the interior United States are in eastern Oklahoma, southeastern Kansas, southern Missouri and Illinois, and the southern half of Kentucky, but the species is absent in much of the Appalachians. Cave and archeological remains indicate that the range of the marsh rice rat has extended substantially further north earlier in the Holocene, into eastern Nebraska, Iowa, Indiana, Ohio, West Virginia, and southwestern Pennsylvania.[47] Fossils of the marsh rice rat are known from Rancholabrean (late Pleistocene, less than 300,000 years ago) deposits in Florida and Georgia;[48] remains referred to the extinct subspecies O. p. fossilis are from the Wisconsinan and Sangamonian of Texas and Illinoian and Sangamonian of Kansas.[49] A 2001 study projected that climate change would reduce the range of the marsh rice rat in Texas.[50]

In southern Texas and in Tamaulipas, the ranges of the marsh rice rat and the related Oryzomys couesi meet;[51] in parts of Kenedy, Willacy and Cameron counties, Texas, and in far northeastern Tamaulipas, the two are sympatric (occur in the same places).[52]

Feeding habits

Oryzomys palustris is predominantly omnivorous, but preferably carnivorous, feeding mainly on insects, snails, and crabs, and occasionally on clams, fishes, baby turtles, carcasses of muskrats, deer mice, sparrows, and eggs and young of marsh wrens. These marsh rice rats also eat seeds and parts from plants such as Spartina spp., Tripsacum spp. and Elymus spp.[53]

Behavior and ecology

Rice rats are adept overwater dispersers; studies on islands off Virginia's Delmarva Peninsula show that they readily cross 300-metre (980 ft) channels between islands.[54]

Population size varies dramatically from year to year in southern Texas.[55]

A 1970 study reported that copulatory behavior in the marsh rice rat is similar to that in laboratory brown rats. Before mating starts, "[t]he male pursues the running female from behind."[56] The male then repeatedly mounts and dismounts the female; not all mounts result in an ejaculation. Penetrations only last for about 250 ms, but during mating the penetrations[56] and the intervals between them become longer.[57] Even when a male is satiated after mating, it is able to copulate again when a new female is introduced (the "Coolidge effect").[58] Partly because of resistance by the female, the frequency of ejaculation during mating is rather low in marsh rice rats as compared to laboratory rats, hamsters, and deermice.[59]


This article incorporates public domain work of the United States Government from the reference [60].

  1. ^ a b Linzey and Hammerson, 2008
  2. ^ a b Harlan, 1837, p. 385
  3. ^ a b Audubon and Bachman, 1854, p. 214
  4. ^ Baird, 1857, p. 459
  5. ^ a b Chapman, 1893, p. 44
  6. ^ a b Allen, 1894, p. 177
  7. ^ a b Bangs, 1898, p. 189
  8. ^ Merriam, 1901, p. 277
  9. ^ a b Hibbard, 1955, p. 213
  10. ^ a b Hamilton, 1955, p. 83
  11. ^ a b Hamilton, 1955, p. 85
  12. ^ a b Spitzer and Lazell, 1978, p. 787
  13. ^ Musser and Carleton, 2005, p. 1152; Miller and Kellogg, 1955, p. 430
  14. ^ Carleton and Arroyo-Cabrales, 2009, p. 106
  15. ^ Weksler et al., 2006, table 1
  16. ^ Weksler, 2006, p. 3
  17. ^ Musser and Carleton, 2005
  18. ^ Chapman, 1893, p. 43
  19. ^ a b Audubon and Bachman, 1854, p. 216
  20. ^ Audubon and Bachman, 1854, p. 216; Harlan, 1837, p. 386; Chapman, 1893, p. 43; Goldman, 1918, pp. 8–9
  21. ^ Baird, 1857, pp. 458, 482, 484; Goldman, 1918, p. 9
  22. ^ Goldman, 1918, p. 9; Carleton and Arroyo-Cabrales, 2009, p. 116
  23. ^ Merriam, 1901, pp. 274, 277
  24. ^ a b Goldman, 1918, p. 22
  25. ^ a b Goldman, 1918, p. 26
  26. ^ Dalquest, 1965, p. 70
  27. ^ Merriam, 1901, p. 275; Goldman, 1918, p. 20
  28. ^ Hall, 1960, pp. 172–173
  29. ^ Benson and Gehlbach, 1979, p. 227
  30. ^ Schmidt and Engstrom, 1994, p. 419; Musser and Carleton, 2005, p. 1147
  31. ^ Goodyear, 1991, p. 423
  32. ^ Humphrey and Setzer, 1989, p. 557
  33. ^ Musser and Carleton, 2005, p. 1153
  34. ^ Humphrey and Setzer, 1989, p. 557; Musser and Carleton, 2005, p. 1152
  35. ^ Baird, 1857, p. 482
  36. ^ Goldman, 1918, p. 25
  37. ^ Goldman, 1918, p. 27
  38. ^ Musser and Carleton, 2005, p. 1152; Milazzo et al., 2006
  39. ^ Steward, 1951
  40. ^ Wolfe, 1982, p. 1; Whitaker and Hamilton, 1982, pp. 278–279; Kays and Wilson, 2000, p. 108
  41. ^ Whitaker and Hamilton, 1982, p. 279; Kays and Wilson, 2000, p. 108; Goldman, 1918, p. 22
  42. ^ Whitaker and Hamilton, 1998, p. 279; Wolfe, 1982, p. 1; Goldman, 1918, p. 20
  43. ^ Kays and Wilson, 2000, p. 108
  44. ^ Humphrey and Setzer, 1989, p. 558
  45. ^ Humphrey and Setzer, 1989, pp. 563–564
  46. ^ Musser and Carleton, 2005, p. 1152; Wolfe, 1982, p. 1; Schmidt and Engstrom, 1994, p. 914
  47. ^ Wolfe, 1982, p. 1; Musser and Carleton, 2005, p. 1142
  48. ^ Weksler, 2006, p. 88; Wolfe, 1982, p. 1
  49. ^ Wolfe, 1982, p. 1; Hibbard, 1955, p. 213; Dalquest, 1962, p. 575; 1965, pp. 63, 70
  50. ^ Cameron and Scheel, 2001, table 3, pp. 668–669
  51. ^ Schmidt and Engstrom, 1994, p. 914
  52. ^ Schmidt and Engstrom, 1994, p. 916
  53. ^ USFWS 1999, page 179.
  54. ^ Forys and Duesser, 1993, p. 411
  55. ^ Schmidt and Engstrom, 1994, p. 917
  56. ^ a b Dewsbury, 1970, p. 268
  57. ^ Dewsbury, 1970, p. 269
  58. ^ Dewsbury, 1970, p. 271
  59. ^ Dewsbury, 1970, p. 274
  60. ^ U.S. Fish and Wildlife Service. (18 May 1999). South Florida multi-species recovery plan. U.S. Fish and Wildlife Service, Atlanta, Georgia. 2172 pp. Caption "Rice Rat Oryzomys palustris natator". 767-786.

Literature cited

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